This invention relates generally to air cooling or air conditioning systems. More specifically, the invention relates to a method and apparatus for determining the relative humidity of air entering the cooling heat exchanger of an air conditioning system.
It is well known that environmental comfort level is not just a function of temperature. Other factors, such as carbon dioxide level and the presence of smoke, dust, pollen and other pollutants can also be detrimental to air quality. One important contributor to comfort level is relative humidity. For optimum comfort, the relative humidity of the surrounding air must be maintained within a certain range. Control of relative humidity is important not only because of its effect on human comfort but also because either excessively moist or excessively dry conditions can be detrimental to equipment, furniture, buildings and the like.
Advances in the air conditioning art have led to the ability to more precisely and independently control not only air temperature in a conditioned space but also other variables such as relative humidity. One such advance is an air conditioning system having a variable cooling capacity. This capability is achieved in newer, more sophisticated vapor compression systems by providing variable speed motors to drive the compressor and heat exchanger fans. Proper control of such systems to achieve desired relative humidity levels requires that the relative humidity in the conditioned space be known. A control device can then use that information together with other parameters, such as temperature, of the air in the space to determine the proper operating mode for the system.
Most hygrometric devices have one or more of the attributes of being expensive, bulky and unreliable, all of which are undesirable in an air conditioning system. What is needed is a simple and inexpensive way to determine the relative humidity of the air in the conditioned space so that the controller of the system can take the proper action to bring and maintain the relative humidity within a desired range.